Remote-control metering system



April 22, 1947 w. R. DREssr-:R 2,419,487

REMOTE CONTROL METERING SYSTEM Filed Feb. 2. 1944 3 sheets-sheet 1- ImOVSKW O f7 7' TUR/VE),

' April 22, 1947. w. R. DRI-:ssen 2,419,487

REMOTE CONTROL IIETRING SYSTEM Filed Feb. 2, 1944 5 Sheets-Sheet 2INVENTOR. CHN /N' /'PP/FTUS s V 7 `imm @MM/wer April 22, 1947. w. n.DREssER 2,419,487

REMOTE CONTROL METERING SYSTEM Filed Feb.v 2, 1944 3 Sheets-Sheet I5ffm/mam 2m ,17 v

caw/fm mmm .SW/0N Patented Apr. 22, 1947 REMOTE-CONTROL METERING SYSTEMWillis Robert Dresser, Long Hill, Conn., assignor to Kenyon InstrumentCo., Inc., Huntington Station, Long Island, N. Y., acorporation of NewYork Application February 2, 1944, Serial N0. 520,815

12 claims. l

This invention relates \to remote control Systems and h'as for itsobject to provide a novel and improved electrical system Vforcontrolling the operation of apparatus at a distant point and forautomatically.transmitting an answering signal to indicate the conditionof such apparatus to the attendant at the control station.

Another object of the invention is to provide a remote control system.for scanning an instrument such as a thermometer, barometer, pressuregauge or the like,l located at a remote point such as an unattendedweather station, and for promptly reproducing an accurate reading ofsuch instrument at the distant control station.

Another object is to provide a system of the above type which isoperated by alternating current impulses and in which all of theconnections between the stations maybe effected by means of aconventional telephone line or radio link, with no more supervision oreffort than is `required to initiate an ordinary telephone call.

Still another object is to provide a system of the above type with a newand improved scanning apparatus including a simple and accurate means tocompensate for non-uniform calibrations of the thermometer, barometer,water-level gauge or other instrument which is to be scanned.

Various otherobjects and advantages will be apparent as the nature ofthe invention is more fully disclosed. u

For the sake of simplicity I` shall describe th'e inventionv in itsapplication to a system for transmitting and recording temperaturereadings at a distant point, although it will be evident as thedescription progresses that the invention is equally applicable to' thetransmission of information regarding humidity, pressure, water level,etc., as Well as a varietyof other purposes.

It will/be assumed that the attendant 'at a central weather bureaudesires to take the reading of a thermometer located atan unattendeddistant sub-station, for example, on the top of a mountain, which isequipped with ordinary telephone toll service for occasional use byforest rangers, hunters or the like. According to my invention theattendantat the central control station, by merely dialing or otherwiseringing the unattended station, will automatically operate apparatuswhich will scan the thermometer and immediately transmit the correctreading back to the control station where it is recorded on a dial orother suitable instrument.

Important novel features of the' inventioninclude the provision of meansat the remote substation for insuring the proper initial setting of 2the scanning apparatus at the start of each ca in case it was notproperly set at the conclusion of th'e preceding call; a novel electriccircuit at the sub-station including a special arrangement of relays foreffecting the proper sequence of l operations and insuring the faithfultransmission of signalling impulses for operating the recordinginstrument at the control station in step with the scanning apparatusafter it has once been set at the starting position; and variousfeatures in the construction and operation of the scanning apparatusitself, particularly the provision of means for compensating for thenon-linear calibrations of the thermometer or other instrument to bescanned, whereby the impulses transmitted back to the control stationwill be of proper duration and will insure the faithful' and accuratetransmission and reproduction of the desired readings.

Although the novel features which are characteristic of this inventionare set forth more in detail in the claims appended hereto, the natureand scope of the invention may be better understood by referring to thefollowing description, taken in connection with the accompanyingdrawings forming a part thereof, in which certain specific embodimentshave been set forth for purposes of illustration.

In the drawings: 1

Fig. 1 is a diagrammatic view of the electrical circuits and apparatuslocated at the sub-station containing the thermometer or otherinstrument to be scanned; i

Fig. 2 is a. side view of the instrument panel at the sub-station,including the thermometer and a vertically movable carriage containingthe 'scanning and associated apparatus;

Fig. 3 is a top plan view of the apparatus shown in Fig. 2;

vpartly broken away to illustrate the operating mechanisms; and l Fig.'7 is a perspective view illustrating a modiiication of the inventionemploying a dial-type meter, such as a barometer, in place of the linearthermometer oi' Fig. 2.

In the following description certain specific 'terms are used forconvenience in referring to the various details of the invention. These3 terms, however, are to be interpreted as broadly as the state of theart will permit.

Scanning apparatus I shall rst describe the scanning apparatus shown inFigs. 2 to 5, which is assumed to be located at an isolated unattendedsub-station of a weather bureau or the like.

At this sub-station there is an instrument box or panel I containing anupright thermometer 2 of standard construction having the usual mercuryor other iluid column 3.

The apparatus for scanning thermometer 2 is mounted on a verticallymovable carriage 4 having rollers which run on vertical tracks 5 securedto opposite sides of the instrument panel Iy as shown in Figs. 2 and 4.

Suitable counterweights I are secured to cords 8 which pass over pulleys9 on the top of panel I and are tied to the vertically movable carriage4 by loops I0, as shown in Fig. 2. Hence when the carriage 4 is releasedby a locking device hereinafter described, and permitted to ride freelyon its tracks 6, the counterweights 'I will descend and thereby raisethe carriage to the top of the panel I.

The scanning apparatus mounted on carriage 4 includes an exciter lamp I2and lens I3 on one side of thermometer 2, and a photoelectric cell I4mounted on the opposite side of said thermometer, The lens I3 focusesthe rays from lamp I2 at a point on the mercury clumn 3 of thermometer2, and when the mercury is in the` path of said rays the photoelectriccell I4 is inoperative. I2 are focused at a point on the thermometerabove the column of mercury, the light will strike the photoelectriccell and render it conductive.

As will be hereinafter more fully explained, the scanning operationalways starts with the carriage 4 at the top of panel I, and thethermometeremployed at the sub-station is always such that the mercurywill never rise high enough to obstruct the rays from lamp I2 when thecarriage is at its uppermost starting position.

The mechanism for actuating the carriage 4 includes a vertical toothedrack I5 secured by brackets I6 to the panel I; a stepping solenoid ormagnet I1 mounted on carriage 4 and having an armature lever I8 carryinga pivoted stepping pawl I9 which is normally held by spring 20 inengagement with the teeth of a pinion 2I on shaft 22 journalled incarriage 4; a star wheel or sprocket 23 keyed to shaft 22 and engagingthe teeth of stationary rack I5; a, release solenoid or magnet 24 havingan armature lever 25 adapted to disengage pawl I9 from pinion 2I, and anex- However, when the rays from lamp lIO the teeth of rack I5 areequidistant, as are also the teeth of sprocket 23. However, thecalibrations of thermometer 2 are not al1 uniformly spaced. and thissame condition may also prevail in other types of meters or gaugesemployed in a system of this kind. In the preferred form of theinvention this non-uniformity in the calibrations of thermometer 2 iscompensated or corrected by cutting or forming the teeth of sprocket 23at a slant or diagonally on the edge instead of straight across the edgeof the sprocket, and by bending the teeth of rack I5 when necessary tomake them engage the slanting teeth of the sprocket at certain pointswhich will be determined by the spacing of the calibrations on thethermometer.

Thus in 2 and 5 certain teeth 3|) of the rack I5 are bent sideways outof the flat vertical plane of the rack, in a manner somewhat analogousto the teeth of a rip-saw, while all o the teeth 3i of the sprocket 23are arranged on a slant or diagonal with respect to the sides of saidsprocket. The slanting teeth 3l of the sprocket are equally spaced andare parallel to one another; hence if all the teeth of rack I5 wereunbent and in the at vertical plane of said rack they would all engagethe slanting teeth 3l of the sprocket at precisely the same points.However, the bent teeth of rack I5, being out of vertical alignment withthe plane of said rack, will necessarily engage a different portion ofthe slanting teeth of the sprocket. The extent of bending ol the teeth30 is made to coincide with the increment between the correspondingcalibrations of the thermometer. Such adjustments may easily be made toiit any thermometer or other instrument, as required.

Electrical circuit at sub-station Fig. 1 is a circuit diagram of thesub-station where the thermometer 2 is located. In the embodimentillustrated, this sub-station may be connected to a central controlstation by a transtension 26 of said lever 25 adapted to trip a lockingpawl 2`I which is normally held by spring 28 in engagement with theteeth of pinion 2I.

Accordingly, each time the stepping magnet Il is energized, in a mannerhereinafter described,

it actuates its armature lever I8, causing the pawl I9 to rotate thepinion 2I one step and thereby rotating the sprocket 23 and lowering thecarriage 4 a distance of one measured increment. This increment may beequal to one degree on the scale of thermometer 2. And when the releasemagnet 24 is energized, as hereinafter described, it actuates itsarmature -lever 25. thereby disengaging stepping pawl I9 and lockingpawl 2T from pinion 2l and permitting the coun'- terweights 'I todescend and thus raise the ycarriage 4 to the top of panel I.

In the embodiment illustrated in Figs. 2 to 5 mission medium such as aconventional telephone m11 une 35. 4 f

When the attendant at the control station desires to read thethermometer at the sub-station, he merely dials or otherwise signals thesub-station in the same way that an ordinary telephone call isinitiated.

When a call is initiated in this manner, the low frequency ringingcurrent impressed upon the transmission line 35 passes through band-passfilter 36 at the sub-station and operates the slow release alternatingcurrent relay 3T. This relay 31 establishes an energizing circuit forthe quick make-slow release relay 38, extending from grounded battery39, through conductor 40, contact 31a of relay 31, winding of relay 38,to ground.

Contact 38a of relay 38, in closing, connects the line terminatingresistor 42 across the incoming transmission line 35, therebydiscontinuing the ringing signal. Contact 38h of relay 38 connectsbattery 39 to the exciter lamp l2; it also completes an energizingcircuit for the filament of vacuum tube amplier 43, extending fromgrounded battery 39, through conductor 4D, contact 38h of relay 38,conductor 44, the filament of amplier 43, resistor 45, to ground.Although the ringing signal was discontinued when resistor 42 wasconnected across the line 35, the relay 38 is designed to have asufiiciently slow release to allow the filament of amplier 43 to bewarmed up and a holding circuit established for relay 38 as hereinafterdescribed before the relay releases.

In the meantime, the closing of contact 38h of relay 38 establishes anenergizing circuit for the release magnet 24 oi the scanning apparatus,extending from grounded battery 39, through conductor 40, contact 38h ofrelay 38, conductor 44, the normally closed back contact 46c of slowmake-quick release relay 46, conductor 41, winding of release magnet 24,to ground. Operation of the release magnet 24 releases the carriage 4 ofthe scanning apparatus of Fig. 2, permitting the counterweights `I todescend and thereby raise the carriage to its starting position at thetop of the instrument panel I, as previously described. This makescertain that the scanner carriage is released and returned to itsinitial scanningposition before each transmission.

Now, as soon as the lament of the vacuum tube 43 has warmed up, lightyfrom the exciter lamp I2, striking the photoelectric cell I4, rendersit conductive and causes a positive biasing potential to be impressedupon the control grid of tube 43 by battery 48` through resistor 49.This permits the passage of plate current from battery 48 through thewinding of the slow makequick release relay 46, thereby closing relaycontacts 46a and 46h, and opening relay contact 46c. The opening ofcontact 46c breaks the energizing circuit of the scanner releasemagnet24.

The closing of contact 46h of relay 46 establishes a holding circuit forrelay 38, extending from grounded battery 39through conductor 4I),contact 38h of relay 38, conductor 44, contact 46h of relay 46,conductor 50, contact 38C of relay 38, windingv of relay 38, to ground.Thus relay 38 remains energized and its contacts closed even after thediscontinuance of the incoming ringing signal.

'I'he contact 4Gb oi relay 46, in closing, also operates the oscillatoror tone generator 5I over a circuit extending from grounded battery 39,through contact 38h of relay 38, conductor 44, contact 46h of relay 46,the energizing element of oscillator 5I. to ground. It also operates aslow make-slow release relay 52 over a circuit extending from groundedbattery 39, through conductor 40, contact 38D of relay 38, conductor 44,contact 46b of relay 46, conductor 53, the normally closed back contact52h of relay 52, winding of relay 52, to ground.

At the same time, the scanner stepping magnet I1 is energized over acircuit extending from grounded battery 39, through conductor 40.contact 38h of relay 38, conductor 44. contact 46h of relay 46,conductor 53, contact 52h of relay 52, conductor 54, winding of magnetI'I, to ground. The scanner magnet II thereupon moves its stepping pawlI9 and pinion 2I tov permit a displacement of one measured increment.holding until the current to magnet I'I is cut off by the opening ofcontact 52h of relay 52 as a result of the delayed operation of saidrelay 52.

The relay 52, in operating` closes its front contact 52a, thuscompleting the circuit from oscillator 5I through said contact 46a ofrelay 46 and the `contact 52a of relay 52 to the high pass filter 56 andthence to the telephone line 35. As a. result, an outgoing signal ortone is impressed upon the telephone line 35 by the oscillator 5I beforeeach actuation of the scanner stepping magnet II, provided there is nointerruption of the light from the exciter lamp I2 to the phctoelectriccell The opening of the normally-closed back contact 52h of relay 52breaks the energizing circuit of the scanner stepping magnet I1, causingsaid magnet to be reset thereby causing a displacement at one incrementof the scanner current conditioning the magnet I1 to receive the nextcurrent impulse. The opening of relay contact 52b also breaks theenergizing circuit of relay 52, causing a delayed release ofitsarmatures and the restoration of the current now to stepping magnet I1through said relay contact 52h when again closed, thus repeating thetone transmission by oscillator 5I and the stepping of the scanningmechanism as described above.

The foregoing cycle is repeated as long as the light from the exciterlamp I2 is not interrupted in its passage to the photoelectric cell I4.When the scanning cycle is continued to the point where the light fromexciter lamp I2 is interrupted by the column of mercury in thermometer2, preventing light from reaching the photoelectric cell I4, thefollowing cycle of operations is initiated.

When the photoelectric cell I4 is no longer conductive, due to thecessation of light thereto, the positive bias is removed from 'thevacuum tube 43, thus interrupting the flow of current from battery 48through the winding of relay 46 to the plate of the tube 43. This causesrelay 46 to be deenergized, opening contact 46h and thus breaking theholding circuit of the quick make-slow release relay 38. However,because of the slow-release characteristics of relay 38 it will maintainits contact 38h in closed. position for a short time after theinterruption of said holding current; hence contact 38h can again supplycurrent from battery 39 through the now closed back contact 46c of relay46 to the scanner release magnet 24, thereby returning the carriage 4 ofthe scanning apparatus to its Starting position at the top of theinstrument panel I as previously described.

Also, because of the opening of contact 46a of relay 46 and Contact 52aof relay 52, and the interruption of operating current to the oscillator5 I, no further signals will be impressed upon the telephone line bysaid oscillator.

Upon the delayed release of relay 38, the opening of its contact 38adisconnects the line terminating resistor 42 from the line 35. Likewise,the opening of relay contact 38h discontinues the ow of -current to theexciter lamp I2, the vacuum tube 43 and the scanner release magnet 24,resetting the entire system at the sub-station in readiness for thereceipt of a later call.

Recording signals at control station The central control station orweather bureau is represented in the drawing by the recording instrument58 shown in Fig. 6.

This instrument, which may be of any suitable type, is connected to thetelephone line 35 by conductors 59 and includes a stepping magnet 60responsive to the alternating current tone impulse impressed upon theline 35 at the sub-station as previously described.

The stepping magnet 60 has an armature 6I controlling the stepping pawl62 which engages the teeth of a. ratchet wheel 63 mounted on shaft 64.Also engaging the ratchet 63 is a holding pawl 65 pivoted on a stud 66with a separate releasing lever EI and normally urged into engagementwith the ratchet by a, spring 68.

The releasing lever 61 projects out through a slot 69 in the casing ofinstrument 58, and, when this lever is grasped and pivoted about thestud 66 against the tension of spring 1I, a pin 'II carried by the leverforces the holding pawl out of engagement with ratchet 63. When ratchet63 is thus released a helical spring 13 returns the shaft 64 and apointer 14 carried thereby'to an initial starting position correspondingwith the highest possible reading of the thermometer 2 when the carriage4 is at the top of the instrument panel I at the sub-station.

The recording instrument 58 has a calibrated dial face correspondingwith the calibrations on the thermometer 2 at the sub-station. Beforecalling the sub-station the attendant at the central control stationtrips the releasing lever B1 of the,I instrument 58 to set the pointer14 at the starting position. He then signals the sub-station, and, aspreviously described, the rst signal received at the sub-station causesthe operation of the scanner release magnet 24 which sets the scanningapparatus at its proper starting position if not already in suchposition. Hence the instruments at the two stations will be ready tostep in unison at the beginning of the scanning operation.

The signalling impulses impressed upon the line by the oscillator 5I atthe sub-station are received at the central control station, and thestepping magnet 60 of instrument 58, responding thereto, advances thepointer 14 one measured increment for each impulse received. The pointer14 thus moves in step with the descending carriage 4 of the scanningapparatus, and, when the pointer nnally comes to rest upon the cessationof the impulses transmitted by oscillator 5I, it will coincide with thereading of the thermometer 2 at the sub-station.

Dial-type meter of Fig. 7

Fig. '7 illustrates a modication of the invention employing acylindrical dial-type meter 15, such as a barometer, pressure gauge orthe like, in place of the straight glass thermometer 2 of Fig. 2.

The meter 15 may be of any suitable type having a hand or pointer 11which is rotated in an arc or circle in response to changes in airpressure, water level, temperature or any other condition for which theinstrument is intended.

The casing of meter 16 is stationary and it has an arcuate Orcirculartransparent area 'I8 encompassing the eld of movement of the pointer 11,which field is usually considerably less than a full circle.

The exciter lamp I2 and lens I3 and the photoelectric cell I4 aremounted on a rotatable carriage shaft 80 in axial alignment with theshaft of pointer 11, and the parts are so positioned that the light fromlamp I2 will pass through the transparent area 18 of the instrument andimpinge upon the photoelectric cell I4 when said light rays are notobstructed by the pointer 11.

In operation, the shaft 80 carrying the scanning apparatus is rotatedstep-by-step in any suitable manner, usually by a pawl-and-ratchetmechanism of the type previously described. The movement of the carriageceases when the light rays from exciter lamp I2 are intercepted by thepointer 21. The electrical circuit may be the same as that shown in Fig.l, and the recording instrument at the central control station may bethe same as that shown in Fig. 6.

It will be evident that a plurality of remotely controlled units such asthat described above may be operated in parallel, or at the same time byemploying different tones or different operating frequencies for thevarious answer-back oscillators for simultaneous transmission. Such asystem may be employed, for example, for transmitting and recording thereadings of wet and dry bulb thermometers. Likewise a number of scannersmay be employed in tandem, or operated one after another, by theaddition of a following sequence relay selector.

It is to be understood that the above examples are only illustrative andthat various changes may be made therein and that the invention iscapable of various other uses which will be readily understood by aperson skilled in the art.

What is claimed is:

l. In a remote control scanning system including a transmission mediumfor the transmission of signals between a central control station and aremote sub-station, an instrument at said sub-station having a movableelement, a carriage including an exciter lamp and a lightresponsive celladapted to move about the field of said movable element to direct thelight rays from said lamp upon said cell when not interrupted by saidmovable element, means for advancing said carriage in successivemeasured increments from a predetermined starting position, means atsaid sub-station for setting said carriage at said starting positionupon receipt of an incoming signal, and means at said sub-stationresponsive to such incoming signal and operative during the energzationof said light-responsive cell for advancing said carriage and forimpressing signals in step therewith upon said transmission medium fortransmission to said central station.

2. In a remote control scanning system including a transmission mediumfor the transmission of signals between a central control station and aremote sub-station, an instrument at said substation having a movableelement, a carriage including an exciter lamp and a light-responsivecell adapted to move about the field of said movable element to directthe light rays from said lamp upon said cell when not interrupted bysaid movable element, means including a stepping magnet for moving saidcarriage in successive measured increments from a predetermined startingposition, means at said sub-station for setting said carriage at saidstarting position upon receipt of an incoming signal, and means at saidsub-station responsive to such incoming signal during the energizationof said light-responsive cell for actuating said stepping magnet and forimpressing signals in step therewith upon said transmission medium fortransmission to said central station.

3. In a remote control scanning system including a transmission mediumfor the transmission of signals between a central control station and aremote sub-station, a measuring instrument at said sub-station having amovable element adapted to fluctuate in response to changes in theconditions to be measured by said instrument, a light-transmitting areain said instrument in the eld traversed by said movable element, acarriage including an exciter lamp and a light-responsive cell adaptedto move about the eld of said movable element to direct the light raysfrom said lamp upon said cell when not interrupted by said movableelement, means including a stepping magnet for moving said carriage insuccessive measured incrcments from a predetermined starting position,means at said sub-station for setting said carriage at said startingposition upon receipt of an incoming signal, and means at saidsub-station responsive to such incoming signal during the energizationof said light-responsive cell for actuating said stepping magnet andAfor simultaneously impressing signals in step therewith upon l:saidtransmission medium for transmission to said Central station. v

4. In a remote control scanning system including a transmissionmediumfor the transmission of signals between'a central control stationand a remote sub-station, a measuring instrument at said sub-stationhavingV a movable element adapted to fluctuate in response to changes inthel conditions tobe measured by said instrument, a light-transmittingarea in said instrument inthe iield traversed by said movable element, acarriage adapted to move about the eld of said movable element/,anexciter lamp and a light-responsive cell on/said carriage in position todirect the light rays from said lamp to said cell when not interruptedby said movable element, means including a stepping magnet formoving'said carriage in successive measured increments from an initialstarting position, means includingfa releasing magnet for returning saidcarriage to said starting position, means at said sub-station foroperating said releasing magnet momentarily upon receipt of a signal,and means operated.r subsequently upon receipt of such signal and duringthe energization of said lightresponsive cell for actuating saidstepping magnet and for simultaneously impressing signals in step`therewith upon said transmission medium for transmission'to saidcentral station.

5. In a remote control' scanning system including a transmissionmediumfor the transmission of `signals between acentral control stationand a remote sub-station, a measuring instrument at said sub-stationhaving la movable element adapted to fluctuate in response to changes inthe conditions to be measured by said instrument, a light-transmittingarea in said instrument in the iield traversed by said movable element,a carriage adapted to move about the field of said movable element, anexciter lamp and a lightresponsive cell on said carriage in position todirect the light rays from said lamp to said cell when not interruptedby said movable element, means including a stepping magnet for movingsaid carriage in successive measured increments from an initial startingposition, means including a releasing magnet for returning said carriageto said starting positiona relay at said sub-station responsive toincoming signals, means including a releasing magnet for returning saidcarriage to said starting position, a relay at said sub-stationresponsive to incoming signals, a second relay operated by said firstrelay and adapted to actuate said releasing magnet upon receipt of asignal, a vacuum tubev having a lament circuit energized by said secondrelay and a. control element in circuit with said light-responsive cellfor activating said tube when said cell is rendered conductive by thereception of light, a third relay actuated by said vacuum tube, saidthird relay having a back contact in the energizing circuit of saidreleasing magnet and a. front contact completing a holding circuit forsaid second relay whereby to break the 'former circuit and complete thelatter upon the operation of said third relay, a signalling deviceoperated by said third relay, a fourth relay operated by said thirdrelay, said fourthrelay having a back contact in its own energizingcircuit and in the energizing circuit of said stepping mag- -net andhaving a front contact connecting said signalling device to saidtransmission medium whereby to alternately make and break said circuitsunder its control and thereby actuate said stepping magnet in measuredincrements while impressing corresponding signals from said sigactuatedby said relay to operate said releasing sponding signals upon saidtransmission mediumfor transmission to said central station.

6. In a remote control scanning system including a transmission mediumfor the transmission of signals between a central control station and aremote sub-station, a measuring instrument at said sub-station having amovable element adapted to uctuate in response to changes in theconditions to be measured by said instrument, a light-transmitting areain said instrument in the field encompassed by said movable element, acarriage adapted to move about the field of said movable element, anexciter lamp and a light-responsive cell on said carriage in position todirect the light rays from said lamp to said cell when not interruptedby. said movable element, means including a stepping magnet for movingsaid carriage in successive measured increments from an initial startingposition, means ditions to be measured by said instrument, a

light-transmitting area in said instrument in the field encompassed bysaid movable element,

va carriage adapted to move about the eld of said movable element, anexciter lamp and a light-responsive cell on said carriage in position todirect the light rays from said lamp to said cell when not interruptedby said movable element, means including a stepping magnet for movingsaid carriage in successive measured in.. crements from an initialstarting position, means including a releasing magnet for returning saidcarriage to said starting position, a relay at said A light, a thirdrelay of the slow make-quick release type actuated by said vacuum tube,said third relay having a back contact in the energizing circuit of saidreleasing magnet and a front contact completing a holding circuit forsaid second relay whereby to break the former circuit and complete thelatter upon the operation of said third relay, a signalling device op..erated by said third relay, a fourth relay of the slow make-slow releasetype operated by said third relay, said fourth relay having a backcontact in its own energizing circuit and in the energizing circuit ofsaid stepping magnet and having a front contact connecting saidsignalling device to said transmission medium whereby to alternatelymake and break the said circuits under its control and thereby actuatesaid stepping magnet in measured increments and impress correspendingsignals from said signalling device upon ment panel, a measuringinstrument in said ipanel having a movable elemenil adapted to fluctuatein response to changes in the conditions to be measured by saidinstrument, a light-transmitting area in said instrument in the eldencompassed by said movable element, a carriage in said panel adapted tomove about the field of said movable element, an exciter lamp and aphotoelectric cell on said carriage in position to direct the light raysfrom said lamp to said cell when not interrupted by said movableelement, means for moving said carriage in successive measuredincrements from a predetermined starting position, and means forreturning said carriage to said starting position.

9. A scanning apparatus comprising an instrument panel, a stationarymeasuring instrument in said panel having a movable element adapted toiiuctuate in response to changes in the conditions to be measured bysaid instrument, a transparent area in said instrument in the eldencompassed by said movable element, a carriage in said panel adapted tomove about the eld of said movable element, an exciter lamp andraphotoelectric cell on said carriage in position to direct the light raysfrom said lamp to said cell when not interrupted by said movableelement, means including a stepping magnet for moving said carriage insuccessive measured increments from a, predetermined starting position,and means including a releasing magnet for returning said carriage tosaid starting position.

10. A scanning lapparatus comprising an instrument panel, a verticaltransparent instrument in said panel having a fluid column of variableheight, a vertically movable carriage in said panel, an exciter lamp anda photoelectric cell on said carriage on opposite sides of saidinstrument in position to direct the light rays from said lamp throughsaid instrument to said cell when not obstructed by said uid column,means on said panel and said carriage for actuating the latter includinga toothed rack and a cooperating toothed wheel, means including astepping magnet and a holding device for actuating said Wheel in adirection to lower said carriage in measured increments, means includinga releasing magnet for releasing said holding device, and

means operative upon the release of said holding device to raise saidcarriage.

11. A scanning apparatus comprising an instrument panel, a verticaltransparent instrument in said panel having a uid column of variableheight adapted to uctuate in non-linear gradations, a vertically movablecarriage in said panel, an exciter lamp and a photoelectric cell on saidcarriage on opposite sides of said instrument in position to direct thelight rays from said lamp through said instrument to said cell whennotobstructed by said iluid column, a vertical toothed rack on said panel,and a rotatable toothed wheel on said carriage cooperating with saidrack for actuating said carriage, the teeth on said rack and wheel beingspaced and shaped to make their points of mutual contact coincide withthe corresponding gradations of said instrument.

12. A scanning apparatus comprising an instrument panel, a verticaltransparent instrument in said panel having a fluid column of variableheight adapted to fluctuate in non-linear gradations, a, verticallymovable carriage in said panel, an exciter lamp and a photoelectric cellon said carriage on opposite sides of said instrument in position todirect the light rays from said lamp through said instrument to saidcell when not obstructed by said fluid column, a vertical toothed rackon said panel, and a rotatable toothed wheel on said carriagecooperating with said rack for actuating said carriage, the teeth onsaid wheel being slanting and uniformly spaced and certain of the tethof said rack being distorted out of the normal plane of said rack tomake their points of engagement with the slanting teeth of said wheelcompensate for the non-linear'gradations of said instrument.

WILLIS ROBERT DRESSER.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 11,585 Bazin Aug. 22, 18541,919,992 Stewart July 25, 1933 2,197,205 Cooper Apr, 16, 1940 2,091,303Breslford Aug. 3l, 1937 674,213 Oldeid May 14, 1901 1,659,834 PippinFeb. 2l, 1928 2,149,753 Wallace Mar. 7, 1939 2,007,669 Yates July 9,1935 FOREIGN PATENTS Number Country Date e 81,141 German May 18, 1895

